1. Field of the Invention
The present invention relates generally to a hypodermic syringe and, more particularly, to a safety hypodermic syringe, which enables the needle assembly to be automatically received inside the barrel upon a return stroke of the plunger after a rotary motion of the plunger.
2. Description of the Related Art
When disposing of a disposable hypodermic syringe after its service, the person handling the disposable hypodermic syringe may be injured by the protruding needle cannula accidentally. In order to eliminate this problem, safety hypodermic syringes are developed. These safety hypodermic syringes enable the needle assembly to be pulled backwards with the plunger and received inside the barrel after the service. Exemplars of these safety hypodermic syringes are seen in Taiwan Patent Publication Nos. 189436; 356013; 463639; 414085; 384709; 359621; 492328; 467752; 475449; 480185; 497976; 430565; 471322; 332433; 394027; and 447310, and U.S. Pat. Nos. 5,385,557; 4,747,830; 4,677,980; 5,242,400; 4,986,813; 4,947,863; 5,533,975; 5,171,300; 4,944,723, . . . etc.
FIG. 1 shows a safety hypodermic syringe according to the prior art. According to this design, the safety hypodermic syringe comprises a barrel 11, the barrel 11 having a front socket 12 and two raised portions 121 protruding from the inside wall of the front socket 12, a needle hub 13 mounted in the front socket 12, the needle hub 13 having two angled crevices 131 extended to the front side and respectively coupled to the raised portions 121 of the front socket 12, and a bottom retaining hole 132, and a plunger and stopper assembly 14 inserted into the barrel 11 from the rear side, the stopper assembly 14 having a front engagement tip 141 adapted to engage the bottom retaining hole 132 of the needle hub 13. FIG. 2A shows the safety hypodermic syringe assembled. This design of safety hypodermic syringe is seen in U.S. Pat. No. 5,273,543. It has drawbacks as outlined hereinafter.
1. The raised portions 121 of the front socket 12 are respectively stopped at the end of the rear horizontal section of the angled crevices 131 when the safety hypodermic syringe assembled. When removing the needle hub 13 from the front socket 12 after the service of the hypodermic syringe, the user must rotate the needle hub 13 with the plunger 14 in the assigned direction. When rotating the plunger 14 in the wrong direction, the connection between the needle hub 13 and the raised portions 121 of the front socket 12 is reinforced, unable to remove the needle hub 13 from the raised portions 121.
2. Because the contact 15 between the needle hub 13 and the front socket 12 is a planar contact, the outer diameter of the needle hub 13 must be made to be press-fitted into the inner diameter of the front socket 12 to prevent a leakage. Due to high friction resistance between the outside wall of the needle hub 13 and the inside wall of the front socket 12, the user must employ much effort to the plunger 14 to pull the needle hub 13 and the needle cannula 133 back to the inside of the barrel 11 after the service of the safety hypodermic syringe (see FIG. 2B).
There are known other designs of safety hypodermic syringes that use a screw joint to secure the neck hub in position. These designs are seen in U.S. Pat. Nos. 4,944,723; 4,978,340; 5,171,300; 4,947,863; 4,986,813. Other needle hub positioning designs are seen in Taiwan Patent Publication Nos. 492328; 356013; 359621; 463639, etc., and U.S. Pat. Nos. 5,242,400; 4,747,830; 5,098,390; 5,370,619; 4,911,693, etc. These prior art designs still cannot eliminate the aforesaid drawbacks.
Therefore, it is desirable to provide a safety hypodermic syringe that eliminates the aforesaid drawbacks.
The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a safety hypodermic syringe, which enables the needle assembly to be conveniently received inside the barrel after the service of the safety hypodermic syringe. It is another object of the present invention to provide a safety hypodermic syringe, which enables the needle assembly to be automatically received inside the barrel upon a return stroke of the plunger after a rotary motion of the plunger.
To achieve these and other object of the present invention, the safety hypodermic syringe comprises a barrel, the barrel comprising a body and a socket at a front side of the body; a needle assembly, the needle assembly comprising a needle hub mounted in the front socket of the barrel, the needle hub having a bottom coupling hole, and a needle cannula forwardly extended from the needle hub outside the barrel; and a plunger and stopper unit, the plunger and stopper unit comprising a stopper fitted into the body of the barrel, and an elongated plunger backwardly extended from the stopper to the outside of the barrel and adapted to reciprocate the stopper in the body of the barrel, the stopper having a front engagement tip adapted to engage the bottom coupling hole of the needle hub for enabling the needle assembly to be pulled backwards with the plunger and stopper unit and received inside the body of the barrel. The socket of the barrel has at least one small stub rod protruding from the inside wall. The needle hub of the needle assembly comprises at least one sliding groove formed in the periphery and respectively coupled to the at least one small stub rod of the socket, for enabling the needle assembly to be pulled backwards with the plunger and stopper unit and received inside the body of the barrel after a rotary motion of the plunger relative to the barrel. The at least one sliding groove each has two distal open ends through which the at least one small stub rod of the socket is moved in and out of the at least one sliding groove when the plunger and stopper unit and the barrel are rotated relative to each other, and a positioning portion on the middle between the two distal open ends for engagement with the at least one small stub rod of the socket. Further, the sliding grooves of the needle hub can be made having a substantially U-shaped profile, or a V-shaped profile.